1. Field of the Invention
The present invention relates to outboard motors including a water pump for pumping coolant.
2. Description of the Related Art
Generally, in outboard motors, a water pump for pumping coolant for cooling an engine and so forth is disposed around a connection portion between an upper case defining a section below the engine and a lower case joined to a lower section of the upper case. A drive shaft transmitting rotation of the engine to a propeller shaft passes through the water pump in the vertical direction. An impeller of the water pump is arranged to unitarily rotate with the drive shaft. Thereby, the water pump is directly driven by the drive shaft (for example, see JP-B-3509171).
Since the impeller is generally made up of materials that will be gradually worn or torn, it is necessary to periodically replace the impeller.
However, to replace the impeller of the water pump, heavy maintenance has to be performed such that a boat on which the outboard motor is mounted is taken out of the water and moved to dry land, the connection portion by which the upper case and the lower case are joined together in the outboard motor is disassembled, and the water pump is taken out. It is necessary to detach and attach a large number of bolts and to reseal to waterproof the casing members. Therefore, maintenance is very difficult.
Further, since the water pump is provided in the upper case and the lower case, there is a limit in the diameter of a pipeline member connected to the water pump due to an inside space of each case, thus resulting in a limit in the improvement in the discharge performance of the water pump.